In E-UTRA/E-UTRAN standardized at present, time multiplex is adopted in both an up link (UL) from a terminal to a base station and a down link (DL) from the base station to the terminal. In up link, when the base station receives data from a plurality of terminals, if the reception timings of the data transmitted by the terminals shift, time multiplex cannot efficiently be executed. Thus, in a time multiplex system, the transmission timings of the terminals need to be adjusted so that the base station can receive the data transmitted by the terminals within a given delay.
This is called uplink synchronization (also called timing adjustment, timing alignment, etc.). The operation required for each terminal to achieve uplink synchronization is a RACH procedure (Random Access CHannel procedure). First, an outline of the RACH procedure will be described and then Message 3 transmission on which the invention focuses attention will be described.
[Outline of RACH Procedure]
In E-UTRA/E-UTRAN, the RACH procedure is used in various cases. The use reasons of the RACH procedure are specifically call connection (initial access), Handover complete, message transmission, UL/DL data transmission and reception resuming (UL/DL data resuming), and reconnection (radio link failure recovery).
The initial access is the case where the terminal performs call connection from an idle (RRC IDLE) state. Since the terminal is in IDLE state, uplink synchronization with the base station is not achieved.
The Handover complete transmission is the case where the terminal executes handover and the target base station is notified that the terminal moves to the target base station. The terminal has not connected to the target base station until then and thus here achieves synchronization with the target base station.
UL/DL data resuming is the case where the terminal performing intermittent reception (DRX) starts to transmit or receive UL or DL data. Since uplink synchronization of the terminal is got out after a while, it is necessary to again achieve synchronization.
Radio link failure recovery is the case where after it becomes impossible for the terminal to detect the connected cell, the terminal reconnects to a cell that is newly found (or that has been connected before). The situation resembles initial access.
There are two large types of RACH procedure. One is the case where the terminal selects RACH preamble transmitted to the base station on its own (non-dedicated RACH preamble case) and the other is the case where the terminal uses RACH preamble given from the base station (dedicated RACH preamble case).
The respective operations are shown in (a) and (b) of FIG. 1. The large difference is as follows: In the non-dedicated RACH preamble case, there is a possibility that a plurality of terminals may use the same RACH preamble at the same time and thus a message for checking the presence or absence of collision (Message 4: Contention resolution) is used; in the dedicated RACH preamble case, RACH preamble to be used is assigned by an assignment message (Message 0: RA preamble assignment).
To Message 1 and Message 2, the same applies to all cases, but in Message 3 and Message 4, different data is transmitted in response to each case. Only Handover complete transmission and DL data resuming can use dedicated RACH preamble, because the base station can perform the operation of assigning RACH preamble only in the two cases.
FIG. 2 shows the two procedures. Dedicated RACH preamble is not always used for Handover complete transmission or DL data resuming and non-dedicated RACH preamble can be used.
Another large difference between non-dedicated RACH preamble and dedicated RACH preamble is that when the base station receives dedicated RACH preamble, it can identify the terminal. Accordingly, work for checking which terminal sends RACH preamble in the later message becomes unnecessary.
In other words, in the non-dedicated RACH preamble case, the ID of the terminal needs to be contained in Message 3 to indicate which terminal accesses. As the ID of the terminal, if the terminal is active (RRC_CONNECTED), C-RNTI (Controlling Radio Network Temporary Id) used in cell units is used; if the terminal executes initial access, S-TMSI (S-Temporary Mobile Subscriber Id entity) used in Tracking area (unit of move management of IDLE terminal) or IMSI (International Mobile Subscriber Identity) of the ID unique to the terminal (corresponding to telephone number) is used. In radio link failure recovery, the cell identifier (cell ID) of the cell connected before radio link failure is caused to occur, C-RNTI in the cell, etc., is used.
[Message 3 Transmission]
Data that can be initially transmitted to the base station by the terminal is Message 3, and information for this is assigned in Message 2. However, it is known that the size of Message 3 is about 72 bits if the terminal is in a cell edge.
Thus, it is considered that it is difficult to transmit all information at one time. To show how Message 3 is configured, FIGS. 3, 4, and 5 show header configurations of MAC (Medium Access Control), RLC (Radio Link Control), and PDCP (Packet Data Convergence Protocol) respectively. FIG. 14 shows the configuration of protocol. An outline is described below:
(MAC)
Three types of MAC sub-headers are provided and the minimum sub-header is eight bits. What data is contained is indicated using LCID (Logical Channel ID), whether or not a MAC sub-header exists following a MAC sub-header is indicated in an E (Extention) field), and the data size is indicated in an L (Length) field).
MAC control element (MAC control information: as up link, C-RNTI, Buffer status report (BSR indicating the buffer status of the terminal), and CQI (Channel Quality Indicator indicating the channel status of the terminal) are also indicated in LCID. In this case, the size is predetermined and thus the L field is not required.
(RLC)
A 16-bit header is defined for RLC AM (acknowledge mode) and 16 bits (10-bit SN for long data) and eight bits (five-bit SN for short data) are defined for RLC UM (unacknowledged mode).
(PDCP)
Different headers are defined in SRB (signalling radio bearer: Bearer for carrying an RRC message of a control message) and data radio bearer (DRB, bearer for carrying data). For SRB, a 40-bit header becomes necessary.
The data radio bearer may be called user plane radio bearer (user radio bearer).
It is considered that Handover complete contains message type (indicating the type of message), transaction id (indicating response to which message), etc., as RRC message, and eight bits are assumed.    Non-patent Document 1: TS25.321: “Medium Access Control (MAC) protocol specification”